Generally, everyone hold a view that magnet adsorb stainless steel tube in order to verify its quality and authenticity. If the magnet does not adsorb stainless pipe, then, it is considered as a good stainless steel
pipe. If not, it is considered as a fake stainless steel pipe. As a matter of fact, this is a very one-sided, crackpot and wrong way. There are many types of stainless steel pipes. It can be divided into several categories according to the organizational structure as follows:
1. Austenite size (martensite): 304, 321, 316, 321, etc.
2. Martensite or transferrin size (austenite): 430, 420, 410, etc.
Austenite is non-magnetic or low-magnetic, while martensite and ferrite are magnetic.
Stainless steel pipe material usually adopts austenite 304. Generally speaking, it is non-magnetic or low-magnetic. However, it is magnetic if chemical composition fluctuates by smelting or the processing status is different. But, it cannot be considered as a counterfeit or substandard stainless steel pipe. What reason is this?
What are mentioned above is that austenite is non-magnetic or low-magnetic, and martensite and ferrite is magnetic. Due to improper smelting composition segregation or heat treatment, it can cause a small amount of martensite or ferrite organization of austenite 304 stainless steel pipe. So, 304 stainless steel tube will be low-magnetic.
In addition, the organization structure of 304 stainless steel tube will transform to martensite after cold working. The greater the deformation degree of cold working is, the more magnetic the steel is. For example, as the same number of steel strip, there is no obvious magnetic when producing Φ 76 tube. However, when producing Φ 9.5 steel pipe, there is much stronger magnetic due to the deformation by cold working. This is because rectangular tube transformation is much bigger than that of circular tube, especially in the angle parts.
To eliminate 304 steel pipe magnetism caused by the above reasons, it can be used by high temperature solid solution treatment. Then, it can recover the austenitic organization stability so as to eliminate the magnetism.
This tells us that if the stainless steel strip is low-magnetic or completely magnetic, the material should be distinguished as 304 or 304. If the magnetism is the same with carbon steel magnetism, and it is strong magnetic, then, it is not 304
stainless steel pipe.
